The basic image-forming process of color negative photography involves the exposure of the silver halide photographic recording material to light, and the manifestation of the recorded image by treatment of the material with a series of aqueous chemical processing solutions. The fundamental steps of this processing entail, first, color development of the recording material wherein some or all of the silver halide is reduced to metallic silver forming an organic dye from the reaction of oxidized color developer and incorporated coupling compounds, and, second, the removal of the metallic silver and residual silver halide by the steps of bleaching and fixing. Herein, the metallic silver is oxidized by a ferricligand complex in the bleach, and the silver ion derived from bleaching, as well as the remaining silver halide, are dissolved away by conversion to a soluble silver complex by the fixing agent.
It is highly desirable to process a photographic recording material as rapidly as possible. The post-development silver removal steps in fact consume more than half of the total process time already, and shortening this segment of the process appears opportune. But juxtaposed with this desire to increase processing speed is the problem that the processing solutions employed in the commercial trade are generally less effective and potent as used in practice than their initial fresh composition would indicate, due to the deleterious effects of process seasoning and underreplenishment. In particular, the performance of the bleach solution is degraded by carryover of the developer solution into the bleach solution, resulting not only in dilution of the bleach solution, but also drift from its optimum low pH by neutralization caused by the basic, high pH developer. The effectiveness of the bleach is diminished, and metallic silver retention occurs, reducing the quality of the resultant photographic image. A useful approach to ameliorate such poor bleaching is to incorporate a bleaching accelerator in the photographic recording material itself.
Light sensitive color negative photographic materials generally comprise three color units or records, each sensitive to a different region of the electromagnetic spectrum. A typical arrangement is to provide a color record comprising an emulsion sensitive to red light having in reactive association a cyan dye forming coupler, a color record comprising an emulsion sensitive to green light having in reactive association a magenta dye forming image coupler, and a color record comprising an emulsion sensitive to blue light having in reactive association a yellow dye forming image coupler.
The use of more than one light sensitive layer in a color record is well established in the photographic arts. Use of three layers each sensitized to the same spectral region but differing in degree of sensitivity is described, for example, in U.S. Pat. No. 3,843,369. Such an arrangement is also known as a "triple-coat". This arrangement is preferred in some circumstances because it is said to provide desirable granularity characteristics.
The incorporation of compounds that release solubilized aliphatic or solubilized aromatic mercaptans as a bleach accelerator directly into photographic recording materials is taught in the art. European Patent 0,193,389A discloses the use of compounds capable of releasing solubilized aliphatic and aromatic mercaptans as bleach accelerator releasing compounds (BARCs). This publication does not specifically describe the use of BAR compounds in triple-coat structures.
More recently, European Patent 0,456,181 has described the use of BARCs in multilayer, multicolor films employing triple-coated records. This usage is said to provide improved bleaching. The examples specifically disclosed in this publication illustrate the localization of the BARCs in the most light sensitive layers of the triple-coated records or the indiscriminate addition of BARCs to many layers of the film. Compounds capable of releasing solubilized aliphatic or solubilized aromatic mercaptans as a bleach accelerator are described.
Japanese Kokai 02/113,242 also discloses the use of BARCs in triple-coated red or green light sensitive color records and specifically recommends localizing the BARCs in the most light sensitive layers of a red or green color record so as to provide improved bleaching characteristics. Compounds capable of releasing solubilized aliphatic or solubilized aromatic mercaptans as bleach accelerator are described.
U.S. Pat. No. 4,865,959 again discloses triple-coated red light sensitive color records. It teaches that bleaching and color reproduction can be improved by selecting a specific and narrow sub-class of cyan dye-forming image couplers and by simultaneously incorporating BARCs in the most light sensitive layer of the triple-coat structure. Compounds capable of releasing solubilized aliphatic or solubilized aromatic mercaptans as bleach accelerator are described.
Compounds capable of releasing solubilized aliphatic mercaptans incorporated in multicolor photographic recording materials as agents to reduce processing variability have been disclosed in publications of foreign counterparts to U.S. patent application Ser. No. 708,546, filed on 31 May 1991. Such incorporation has been carried out in the highest sensitivity blue sensitive layers or distributed between the high and low sensitivity layers of a 2-layer blue sensitive color record. The level of bleach accelerator is less than that required to detectably improve the bleachability of the photographic recording material. This application does not teach improved bleachability.
The incorporation of compounds capable of releasing solubilized aliphatic or solubilized aromatic mercaptans as a bleach accelerator directly in the photographic recording material at a level that is effective in ameliorating seasoned bleach performance can have pronounced side effects on the sensitometric performance and color reproduction performance of the material, however. In particular, the developability of the light sensitive unit(s) incorporating the accelerator can increase, resulting in an increased contrast or gamma function (henceforth gamma) for the color record involved. In turn, the increased developability or rate of development of the color unit can reduce or completely eliminate the interlayer chemical inhibition interactions between color units that results in good color saturation and hue reproduction. Thus the tone scale and color reproduction of the recording material may be severely compromised by measures necessary to ensure adequate bleachability.
A problem to be solved is to provide a photographic element and process which will produce images having improved color reproduction and which will enable improved silver bleaching, particularly in the instance where seasoned bleach is employed during processing.